Developer Patrick Kennedy in the living area of his SmartSpace unit. Developer Patrick Kennedy has built a prototype micro-apartment in a Berkeley storage warehouse. On Tuesday, San Francisco Supervisors approved building of the units in the city.

Photo: Brant Ward, The Chronicle

Developer Patrick Kennedy in the living area of his SmartSpace...

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Patrick Kennedy in the living area of his SmartSpace apartment, the sofa turns into a bed. Developer Patrick Kennedy has built a prototype micro-apartment in a Berkeley storage warehouse.

Photo: Brant Ward, The Chronicle

Patrick Kennedy in the living area of his SmartSpace apartment, the...

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Renderings show the units on Mission Street, planned for 2014 availability, that have a streamlined, cruise ship cabin look. (SMARTSPACE)

Renderings show the units on Mission Street, planned for 2014...

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You would be sleeping directly across from your kitchen sink. (SMARTSPACE)

You would be sleeping directly across from your kitchen sink....

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This overhead view shows how neatly everything fits into the tiny space. (SMARTSPACE)

This overhead view shows how neatly everything fits into the tiny...

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The units can also be configured with two twin beds. (SMARTSPACE)

The units can also be configured with two twin beds. (SMARTSPACE)

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This Harriet Street building is nearly complete, and comprises 23 330-square-foot units. (SMARTSPACE)

Up to two people will be allowed to live in the micro-apartments, which legislation sponsor Supervisor Scott Wiener said would help those who want to live alone but can't afford most of the studio apartments on the market.

"To confront San Francisco's rising housing affordability crisis, we must be creative and flexible," Wiener said in a statement. "Allowing the construction of these units is one tool to alleviate the pressure that is making vacancies scarce and driving rental prices out of the reach of many who wish to live here."

But for the legislation to pass, Wiener had to agree to cap the number of micro-apartments at 375. Under the legislation, the City Planning Department will analyze the effects of the new units once 325 of them are built.

"Family-sized housing is important and its development should be encouraged," Wiener said. "But many - including seniors, students and transition age youth - do not need as much space or cannot afford it. These units will be a viable alternative for those who don't want to live with roommates."

The SoMa neighborhood and other densely populated city locations would be the likely location for the new units, which include a living room, kitchen and bathroom. Supervisor Jane Kim, who represents SoMa, said that neighborhood's population could increase by 32 percent as a result of unlimited micro-apartments.

The cap seemed to satisfy skeptics who say that micro-units are not the solution to the city's housing problem. Supervisor David Campos, who supported the measure, said he visited one of the proposed units and was struck by how expensive rent would be for such a small space.

Concern about rents

The micro-units are estimated to go for $1,300 to $1,500 a month. The average studio apartment in San Francisco rents at $2,075 a month, according to real estate service RealFacts.

"It's not a lot of space for $1,500," Campos said, adding that he was concerned it could raise rents across the city. "If 220 square feet is going to rent for $1,500, what does that do for the rest of the places in San Francisco?"

Supervisor John Avalos was the lone vote against the proposal, arguing that the city should be more focused on keeping families from moving.

"This doesn't make a lot of sense for the San Francisco I know," he said.

Mayor Ed Lee, who still must sign the measure, told reporters after his monthly question-time session before the board that he hadn't taken a position on micro-apartments yet.

"I'm always concerned whenever people are changing the standards, but I do think there might be good policy reasons," he said.

When the Planning Commission reluctantly approved a cap on the number of units last week, some commissioners worried that limitations would confuse developers. But tenant and affordable housing advocates said the cap was crucial to their support.

Looking at tenants

Ted Gullickson, director of the San Francisco Tenants Union, said he hoped the Planning Department study conducted before the cap is reached would shed light on who is moving into the units.

"If they become urban crash pads for high-tech employees, then we fear they could have a gentrifying effect on the neighborhoods as they get built," he said. "We do have a strong need for family-size housing as well as affordable housing, and we have limited development sites in San Francisco."